A source of gas ions is needed for commercial and residential air handling units. It is known that the presence of gas ions may improve the health and attitude of people exposed to this ion source. It is also known that this gas ion source not produce or contain ozone as this is generally considered hazardous to health. Most air handling equipment has high flow rates and pushes large volumes of air.
U.S. provisional application Ser. No. 60/844,761 (the “'761 application”), which is hereby incorporated by reference herein, disclosed the use of carbon nanotubes operating in a field emission mode as a source of ions operating at atmospheric pressure.
The '761 application describes how gas ions are formed at atmospheric pressure by placing a carbon nanotube film on one or both electrodes and then biasing these electrodes while gas is flowing between them (see FIG. 3 of the '761 application). The bias between the electrodes can be in DC mode or in AC mode. Even a series of electrodes can be used (see FIG. 4 of the '761 application). In order for the carbon nanotubes to emit electrons, the electric field applied to the carbon nanotube layer is on the order of 1 V/micron. This requires small gaps or high electrical potentials on the electrode surfaces. For example, a 1 mm gap requires a voltage of 1000V on the electrodes. This is acceptable for small flow rates such as needed in analytical equipment, but will not work well for applications requiring high gas flow rates.
It is also well known that titanium dioxide (also referred to as titanium oxide, titania or TiO2) can be used to decontaminate air (see, Tracy L. Thompson and John T. Yates. Jr., “Surface science Studies of the Photoactivation of TiO2—New Photochemical Processes,” Chem. Rev. Vol. 106, pp. 4428-4453, (2006); and S. Banerjee et al., “Physics and chemistry of photocatalytic titanium dioxide: Visualization of bactericidal activity using atomic force microscopy,” Current Science, Vol. 90, p. 1378, May 2006). TiO2 is known as a photocatalyst, especially the anatase phase of this material. FIG. 1 shows one mechanism how the titania photocatalyst works. When titanium oxide is exposed to ultraviolet rays, electron and hole pairs are created in the titanium oxide material. These charges diffuse to the surface of the titania. Active species such as oxygen radicals are generated on the surface. The active oxygen radicals oxidize organic contaminants including acetaldehyde (cigarette smell) and biologicals in almost the same way as combustion: converting contaminants into harmless water and carbon dioxide. Other active radicals (both positive-charged and negative-charged) are also formed that may attack other contaminants (not shown).